/Engine/Source/Runtime/AVEncoder/Public/AudioTypes.h
The unencoded audio sample buffer is not guaranteed to be available after callback finishes. The pointer of the encoded audio byte buffer should be valid until the next encode call will happen.
typedef [TFunction](API\Runtime\Core\GenericPlatform\TFunction)< void(const [FAudioSampleBuffer](API\Runtime\AVEncoder\FAudioSampleBuffer) &, const [FAudioByteBuffer](API\Runtime\AVEncoder\FAudioByteBuffer) &AudioBytes)> OnAudioEncodeCallback